Experimental investigation and thermodynamic assessment of the Mo–Ni–Zr ternary system

Abstract

The isothermal section of the Mo–Ni–Zr system at 1100°C was investigated by characterization of eight equilibrium alloys. X-ray diffraction (XRD) and electron probe microanalysis (EPMA) were used to identify the stable phases and obtain their compositions. The Mo–Ni–Zr system was then optimized by means of CALPHAD (CALculation of PHAse Diagrams) technique with the consideration of experimental data obtained in the present work and reported in the literature. The liquid, fcc, bcc and hcp solution phases, were modeled with (sub-)regular solution model. The compound Zr65Mo18−xNi16.5+x (τ1, cF96-Ti2Ni) was described as Zr2(Mo, Ni) based on its crystal structure and solubility range. While τ2 (Zr65Mo27.3Ni7.7) phase was modeled as a stoichiometric compound due to its limited homogeneity range. A set of self-consistent thermodynamic parameters for the Mo–Ni–Zr system was finally obtained. Comprehensive comparisons between the calculated and experimental phase diagram data show that the experimental information is satisfactorily accounted for by the present thermodynamic description. The liquidus projection and reaction scheme of the Mo–Ni–Zr system were also generated by using the present thermodynamic parameters.